China yielded last week to international pressure and appointed an envoy for African Affairs. The hope in Western capitals is that Liu Guijin, a former ambassador to Zimbabwe, will persuade the Sudanese government to end the crisis in its Darfur region. Why are we looking toward China to solve a crisis thousands of miles from its borders? Beijing supports the Sudanese government, which in turn sponsors the Janjaweed militia. The Janjaweed has murdered more 200,000 civilians in Darfur and driven another 2.5 million of them from their homes during four years of conflict. The Associated Press calls Darfur “the world’s largest humanitarian disaster.”

How is China involved in helping the Arab-dominated government kill its black African citizens? It buys about two-thirds of Sudan’s oil exports. About 70% of Sudan’s oil revenues go to its military, which is involved in the mass murders. Yet China’s involvement is not just indirect. China sells arms and aircraft to Sudan in a manner that is almost certainly in violation of the United Nations’s arms embargo. As important, Beijing has used its permanent seat on the Security Council to shield Khartoum from effective action by the international community. This has had the effect of continuing what America terms “genocide.” As Darfur activists Mia Farrow and Ronan Farrow recently wrote, “Beijing is uniquely positioned to put a stop to the slaughter, yet they have so far been unabashed in their refusal to do so.”

So if Beijing is responsible for the acts of the government in Khartoum — and it certainly is under the common understanding of that term — then are there other parties accountable for Darfur because they support the Chinese government? As a theoretical matter, there might be. If an enabler is answerable for another’s acts, then so should a party that enables the enabler.

So who is enabling the Chinese? America and other Western nations do not treat China as just another state; they actively engage Beijing and support it. For three decades it has been our fond hope that the Chinese will make the transition to representative governance and free markets from Maoism and Marxism. We have sought to help in this makeover, and, as a result, we have provided technical and material aid to China. More important, we have also been patient with the Chinese, continually tolerating international conduct that is unacceptable. We have the best of intentions, but we may be producing the worst of results.

The issue therefore arises: At what point do other nations begin to share in Beijing’s culpability? The Farrows link Western support of the Olympics and Beijing’s cynical policy in Sudan. With such an expansive view of responsibility it is not surprising that Ms. Farrow is now organizing a new campaign, Divest for Darfur. The goal is to cut the flow of cash to the Sudanese military. For this purpose activists seek to have Berkshire Hathaway and Fidelity Investments sell their holdings in PetroChina, whose parent company has oil fields in Sudan. The ties between the Janjaweed and these American businesses are hardly direct, but Darfur campaigners essentially make the argument that attenuation does not matter.

They have a point that everything is connected to each other and each link of a chain is crucial.

The shareholders of Berkshire Hathaway did not buy their argument — this month they overwhelming rejected a proxy resolution ordering divestment in PetroChina. The Fidelity Investment proposal is also headed for defeat. Yet the divestment idea is catching on. At the end of April the University of Massachusetts announced that it would divest companies involved in Sudan. Last week in Kansas, Governor Sebelius signed a law ordering the state’s largest pension fund to stop investing in companies, including PetroChina, doing business in Sudan. The legislation, modeled on a California law, also requires divestment.

So should the United States “divest” China, so to speak? In theory, the principle that applies to pension fund investments should also apply to diplomatic relations. Surprisingly, we have yet to publicly talk about the moral questions that arise from our engagement of China while it helps perpetuate gruesome activities in Africa.

Unfortunately, this is not just some abstract inquiry. These days, the Chinese may say they want the killing in Darfur to stop, yet they are not willing to take steps within their power to end it. During the third week of April China’s Foreign Ministry stated that it still was “not a proper time to discuss sanctions.” It also indicated that it would block the efforts of America and Britain to impose them. Although new sanctions will not automatically bring peace to Darfur, they are a precondition for the restoration of order in this especially troubled area.

So it is clear that Beijing is blocking a solution. By now China has no excuse for supporting the Sudanese government. And until it withdraws its assistance to Khartoum, we should think about all the implications of our engagement of the government in Beijing. After all, China is not just about China anymore.

Mr. Chang is the author of “Nuclear Showdown: North Korea Takes On the World.”